Field of the Disclosure
The present disclosure relates to a method of machining a workpiece using a machine tool and to a machine tool for performing the method, and particularly, relates to a method of machining a workpiece on a machine tool having a bed supported by a plurality of supporting jigs in a state where a position error caused by change of a horizontal level of the bed has been compensated for, and to a machine tool for performing the method.
Background of the Disclosure
A machine tool typically has a bed disposed on a floor of a plant or the like via jack bolts (supporting jigs), and horizontal level adjustment of a reference surface of the bed is performed by adjusting supporting states of the jack bolts. Note that such an adjusting operation tends to be very empirical and is a sensory operation, and therefore the operation requires skills. However, in recent years, a load detection type jack that is capable of detecting a load acting on the jack has been used, which makes the adjusting operation comparatively easy to perform
By the way, the horizontal level of the bed of the machine tool is one of factors which have a large influence on accuracy in machining a workpiece. If a workpiece is machined in a state where the horizontal level is outside a predetermined range, there occurs a problem that the machining accuracy is deteriorated. Therefore, as described above, machining of a workpiece is typically performed in a state where the horizontal level of the bed reference surface of the machine tool has been adjusted. However, for example, if, after some time has passed since horizontal level adjustment, the horizontal level is changed due to a secular change of a structure, a change of surrounding environment, or the like, and therefore exceeds a predetermined range, it is not possible to accurately machine a workpiece.
Accordingly, for example, there has been proposed an automatic leveling apparatus for machine tool as disclosed in Japanese Unexamined Patent Application Publication No. H04-336927 as an apparatus which, when the horizontal level of the bed has been changed, automatically adjusts a horizontal level of a bed so that the horizontal level falls within a predetermined range.
This automatic leveling apparatus includes leveling detecting means that detects a level change of the bed, a plurality of leveling blocks that are disposed below the bed and are configured to be driven by their respective hydraulic cylinders, and control means that controls the hydraulic cylinders in accordance with a signal relating to the level change detected by the leveling detecting means.
According to this automatic leveling apparatus, the necessity of level correction is determined based on whether the level change detected by the leveling detecting means is within a predetermined range or not, and when the level change is not within the predetermined range and level correction is therefore needed, the hydraulic cylinders drive their respective leveling blocks under control by the control means, whereby leveling is automatically performed.